Photographic processing apparatus

ABSTRACT

An apparatus in which a viscous photographic, processing liquid is distributed in a thin layer between an exposed photosensitive element and another element by moving the elements in superposition through a convergent passage between a pair of juxtaposed pressure-applying members. The viscosity of the liquid varies inversely with temperature. The speed of movement of the elements is constant while the pressure-applying members are biased toward one another with a force that is varied in inverse relation to the ambient temperature to insure uniform liquid distribution despite temperature changes.

, United States Patent [72] Inventor Richard J. Chen Winchester, Mass![21 Appl No, 738,954

[22] Filed June 21, 1968 [45] Patented June 29, 1971 [73] AssigneePolaroid Corporation Cambridge, Mas.

[54] PHOTOGRAPHIC PROCESSING APPARATUS 8 Claims, 4 Drawing Figs.

[52] 0.8. CI 95/89, 95/ l 3 [5| Int. Cl 603d 9/02 [50] Field ofSearch95/89, l3, 14

[56] References Cited UNITED STATES PATENTS 3,108,525 10/1963 Eburnetal.

3,264,963 8/1966 Finelli 95/13 3.441437 6/1969 Tiffany 95/13 3,457,8467/l969 Little 95/13 Primary Examiner-Samuel S. Matthews AssistantExaminer-Fred L. Braun AttorneysBrown and Mikulka and Robert E. CorbABSTRACT: An apparatus in which a viscous photographic, processingliquid is distributed in a thin layer between an exposed photosensitiveelement and another element by moving the elements in superpositionthrough a convergent passage between a pair of juxtaposedpressure-applying members. The viscosity of the liquid varies inverselywith temperature. The speed of movement of the elements is constantwhile the pressure-applying members are biased toward one another with aforce that is varied in inverse relation to the ambient temperature toinsure uniform liquid distribution despite temperature changes.

PATENTEUJUM29|97| 3589.262

SHEET 2 OF 2 IOG FIG.4

INVENTOR. c'cland ffiim ammm ATTORNEYS PHOTOGRAPHIC PROCESSING APPARATUSln photographic apparatus for exposing and processing photographic sheetmaterial, and particularly in portable, handheld, self-developingcameras, an exposed photosensitive element is treated in an externallydry process, preferably to produce a positive photographic print formedby diffusion transfer, by distributing a viscous thixotropie liquid in athin layer between the photosensitive element and another element. Theprocessing liquid may be provided initially in a rupturable pod orcontainer coupled to one of the elements and is distributed between theelements by moving them in superposition together with the rupturablecontainer through a convergent passage between a pair of juxtaposedpressure-applying members. f

For optimum results, measured for example in terms of image quality anduniformity, as well as reliability and re peatability, and particularlywhen the quantity of processing liquid available is limited toapproximately the minimum amount of liquid required, the layer ofprocessing liquid distributed between the elements in contact with thephotosensitive element should be of uniform, predetermined thickness.When the liquid is distributed by moving the elements through aconvergent passage between a pair of pressure-applying members that arefree to move apart from one another and are resiliently biased towardone another,'the thickness of the layer of liquid is dependent upon anumber of factors, including the pressure exerted by thepressure-applying members, the viscosity of the processing liquid, andthe speed of movement of the elements through the passage between thepressure-applying members. The nature and composition of the processingliquid are such that the viscosity of the liquid varies with changes intemperature and since the thickness of the layer of the processingliquid is, in large part, dependent upon the viscosity of the liquid, aproblem arises in apparatus such as self-developing cameras which can becarried and employed both indoors and out and are likely to be employedunder a wide range of temperature conditions.

An object of the invention is to provide photographic apparatus andmethods of the type described in which the speed of movement of a filmassemblage between the pressure-applying members is maintainedsubstantially constant and the compressive force exerted on the filmassemblage by the pressure-applying members is varied in inverserelation to the ambient temperature to compensate fortemperature-related changes in the viscosity of the processing liquidand thereby provide for distribution of the processing liquid in a layerof predetermined thickness despite changes in ambient temperature andthe viscosity of the liquid.

Other objects of the invention will in part be obvious and will in partappear hereinafter.

The invention accordingly comprises the process involving the severalsteps and the relation and order of one or more of such steps withrespect to each of the others, the apparatus possessing theconstruction, combination of elements and arrangement of parts which areexemplified in the following detailed disclosure, and the scope of theapplication of which will be indicated in the claims.

For a fuller understanding of the nature and objects of the invention,reference should be had to the following detailed description taken inconnection with the accompanying drawing wherein:

FIG. 1 is a somewhat schematic, sectional view of a camera embodying theinvention showing a film assemblage and illustrating the process of theinvention:

FIG. 2 is a perspective view showing components of the camera of HO. 1;

FIGS. 3 and 4 are elevational views of components of the cameraillustrating other embodiments thereof.

The photographic apparatus and process of the invention find particularutility in the treatment of photographic film assemblages of the typeincluding all of the materials required to produce a finishedphotographic print, preferably in full color,

and including a photosensitive image-recording element adapted to beexposed to produce an image; a second, or image-receiving elementadapted to be superposed with the photosensitive element, at leastduring processing to aid in the distribution of a viscous processingliquid in contact with the exposed photosensitive element and preferablyto support the visible image formed by diffusion transfer; and arupturable container of viscous processing liquid adapted, whendistributed in contact with the exposed photosensitive element, toproduce a positive image by a process in which image-forming substancesare transferred by diffusion from an exposed photosensitive stratum toan image-receptive stratum. Film assemblages of this type may take anumber of different forms including, for example, separatephotosensitive and second sheets adapted to produce a single print or aplurality of prints; or individual film units each including a pair oflayers ofsheets coupled with or secured to one another in face-to-facerelation and adapted to be exposed and processed to produce a singleprint. The processing liquid may be supplied in a rupturable containercoupled with one or both elements and adapted to be moved together withthe superposed elements through a passage between a pair of juxtaposedpressure-applying members; or the liquid may be supplied from a sourcenot associated with the superposed elements and dispensed between theelements for subsequent spreading in a thin layer during movement of theelements between the pressure-applying members.

The camera and process embodying the present invention are speciallyadapted for the treatment of photographic film units of the type shownand described, for example, in the copending US. Pat. application ofEdwin H. Land, Ser. No. 622,287, filed Mar. 10, 1967, now Pat. No. 3,511,855. A typical film unit of this type includes all of the materialsand reagents required to produce a full color, photographic print by aprocess such as disclosed in US. Pat. No. 2,903,606, issued May 9, I961,in the name of Howard G. Rogers. This patent discloses a photosensitiveelement including a silver halide emulsion and a dye developer, that is,a dye which is a silver halide developing agent; a second orimage-receiving element, including an image-receptive layer of a dyablematerial; and a processing liquid in which the dye developer is solubleand reactive. The photosensitive and image-receiving elements aresuperposed with the emulsion and image-receptive layers in face-to-facerelation and the processing liquid is distributed in a uniform layer ofpredetermined thickness between and in contact therewith for permeationinto the photosensitive layer to initiate development of exposed silverhalide. The dye developer is immobilized or precipitated in exposedareas as a consequence of development, while in unexposed areas orpartially exposed areas of the emulsion, the dye developer remainsunreacted and diffusible, thereby providing an imagewise distribution ofunoxidized dye developer which transfers, at least in part, by diffusionto the image-receptive layer without altering the imagewise distributionof the developer, to form a reversed or positive color image of thedeveloped latent image in the emulsion. Multicolor transfer images areobtained utilizing dye developers, for example, by employing an integralmultilayer photosensitive element such as illustrated in H6. of the2,983,606 patent, including at least two selectively sensitizedoverlying photosensitive strata on a single support. A typicalphotosensitive element of this type comprises a support carrying a redsensitive silver halide emulsion stratum, a green sensitive halideemulsion stratum and a blue sensitive halide emulsion stratum, eachemulsion having associated therewith, respectively, a cyan dyedeveloper, a magenta dye developer and a yellow dye developer, Each setof silver halide emulsions and associated dye developer strata may beseparated from other sets by interlayers formed, for example, of gelatinor polyvinyl alcohol. ln the example given, the dye developers areselected for their ability to provide colors useful in producing a fullcolor image by a subtractive process and may be incorporated in therespective silver halide emulsion with which they are associated or in aseparate layer behind the respective silver hathere is illustrated filmunits of the foregoing type, the

thickness of the materials being exaggerated for purposes of clarity ofillustration. Each film unit, designated 10, comprises a photosensitiveor image-recording sheet 12; a second or image-receiving sheet 14; and arupturable container 16 holding a quantity of processing liquid 18.Sheets l2 and 14 are preferably, although not necessarily, rectangularand coextensive with one another and are arranged in superposed,face-toface contact with at least the lateral edges of each sheetaligned with the lateral edges of the other. The two sheets are retainedin superposedrelation by a binding element 20 in the form of arectangular sheet at least wider than either of the photosensitive andimage-receiving sheets and secured thereto at the margins thereof.Binding element 20 is in the general form of a rectangular frame havinga large rectangular opening 22 defining the extent of the exposed areaof the film unit,

surrounded by lateral edge portions and end portions 24 and 26. Thelateral edge portions and end portion 24 of binding element 20 areadhered, respectively to the lateral and trailing end margins of secondsheet 14 and are secured around the edges of the sheets and adheredrespectively to the lateral and trailing end margins of photosensitivesheet 12, thereby effecposure of the photosensitive sheet and viewing'ofthe image formed between the sheets, the photosensitive sheet is opaqueand a white pigment is provided in the processing liquid to provide awhite background for the transfer image.

Container 16 is of the type shown and described in U.S. Pat No. 2,543,]81 and is formed by folding a rectangular blank of fluid and airimpervious sheet material medially and sealing the marginal sections ofthe blank to one another to form a cavity for containing processingliquid 18. The seal between marginal longitudinal sections 28 of thecontainer is weaker than the end seals so that upon application of apredetermined compressive force to the walls of the container in theregion of the liquid filled cavity, there will be generated within theliquid, hydraulic pressure sufi'tcient to separate longitudinal marginalsections 28 throughout the major portion of their length to form adischarge mouth through which liquid 18 is discharged. Container 16 isattached to sheets 12 and 14 at the leading edges of the sheets,preferably with the longitudinal edge of the container butted againstthe edges of the sheets with the discharge passage of the containeraligned with the facing surfaces of the sheets.

End portion 26 of binding element 20 is secured to the leading marginaledge of sheet 14 and one marginal section 28 of the container, and abinding strip 32 is adhered to the leading marginal edge portion ofsheet 12 and the other marginal section 28 of the container to securethe container to the sheets. Binding strip 32 also cooperates with endportion 26 to provide a conduit for channeling liquid 18 from thecontainer between the sheets at the leading ends thereof.

The embodiment of the film unit illustrated and described 7 herein isadapted to-be exposed and processed to produce a 'multicolor dyetransfer image located between transparent second sheet 14 supporting adyeable polymeric layer and an opaque layer located between the transferimage and the photosensitive medium. This opaque layer comprises theliquid contents 18 of container 16 which are provided in suffirequisitethickness and extent thereby making it unnecessary to provide means forcollecting and retaining excess processing liquid and also providing forminimization of the size of the container and hence the overallsize,'complexity and cost of the film unit. The processing liquidcontained in container 16 comprises an aqueous alkaline solution havinga pH at which the dye developers are soluble and diffusable and containsan opacifyi ng agent in a quantity sufficient to mask the dye developersretained in the image-recording layer (laminate) subsequent toprocessing; and a film-forming viscosity increasing agent or agents tofacilitate rupture of the container and distribution of the liquidprocessing composition and assist in maintaining the layer of processingcomposition as a structurally stable layer tending to bind the sheets toone another.

Subsequent to exposure, film unit 10 is processed by moving the filmunit with the container foremost relative to and between a pair ofjuxtaposed pressurc-applying members into and through a convergentpassage between the members for applying compressive pressure, first tothe container to eject the liquid contents of the container betweenphotosensitive and image-receiving sheets 12 and 14, and then spreadprocessing liquid 18 in a uniform, thin layer between the sheets over anarea at least coextensive with opening 22 in binding element 20. Aspreviously noted, the processing liquid includes an agent for increasingthe viscosity of the liquid so as to promote the opening of thedischarge passage of the container throughout substantially its entirelength and facilitate the discharge of the liquid from the container andspreading of the liquid between the sheets. For this purpose, the liquidshould be quite viscous and contain the film-forming agent in a quantitysufficient to impart a viscosity in'excess of 1,000 centipoises at atemperature of 20 C. and preferably of the order of 1,000 to 200,000centipoises at said temperature. The processing liquid is preferablythixotropic, thereby facilitating complete rupture of the bond betweensections 28 of the container comprising the discharge passage andsubsequent spreading of the liquid between the sheets.

A liquid processing composition suitable for incorporation in container16 for use in combination with sheet materials of the type described toproduce a full color transfer image is dis.- closed in the followingexample:

Water cc. Potassium Hydroxide l 1.2 grams Hydroxyethyl cellulose 3.4grams (high viscosity) [commercially available from Hercules Powder Co.,

- Wilmington, Del., under the trade name Natrasol 250]N-benzyl-ot-picolinium l.5 grams bromide Bensotriazole 1.0 gramsTitanium dioxide 40.0 grams The viscosity of an aqueous liquidprocessing composition of the foregoing type varies inversely withtemperature, increasing as the temperature is lowered and decreasing asthe temperature is raised.

A pair of film units 10 are illustrated as comprising part of a filmassemblage or pack adapted to be employed in a handheld camera. The filmassemblage or pack includes a box or container 36 adapted to hold aplurality of film units 10 arranged in stacked relation and includes aforward wall 38 provided with an exposure aperture 40 substantiallycoextensive with opening 22 in binding element 20 and a spring andpressure plate assembly 42 for supporting the film units against theforward wall with the forwardmost film unit located in position forexposure in alignment with aperture 40. Box 36 includes an end wall 44provided with a narrow slot 46 permitting the movement of the film unitsone at a time from the box through the slot.

A camera of the type adapted to employ the film assemblage for exposingand processing the film units thereof is illustratcd in FIG. 1 ascomprising a housing 48 including a rear section 50 for holding andenclosing container 36, and an intermediate wall 51 having an exposureaperture 52 for locating the foreward wall 38 of container 36 in aposition at which the forwardmost film unit is located in properposition for exposure. The camera includes a forward section 54 forsupport ing a conventional lens and shutter assembly 56, mirror 57arranged in a plane at 45 to the film plane and lens axis for reversingthe image formed by the lens on the film.

The preferred means for spreading the processing liquid between thesheets of a film unit comprise a pair of juxtaposed, pressure-applyingmembers in the form of cylindrical rolls 48 and 60, cooperating todefine a convergent passage or throat through which the sheets are movedin superposition with container 16 foremost, to dispense the liquidcontents of the container between the leading end portions of the sheetsand then distribute the liquid from the leading end of the sheets towardthe trailing end thereof. As shown in FIG. 2, roll 60 is mounted in asubstantially fixed position for rotation about its axis and roll 58 ismounted for rotation about an axis located in the same plane as the axisof roll 60 and for'movement toward and away from roll 60. Means areprovided for biasing roll 58 toward roll 60 and in the form showncomprise elongated cantilever springs 62, each mounted at one end of thecamera housing and engaged at its other end with a shaft (or the journaltherefor) on one end of roll 58. Means, to be described more fullyhereinafter, are provided for engaging each spring 62 intermediate itsends for biasing the free end of each spring in the direction of roll60.

As previously noted, the thickness of the layer of processing liquiddistributed between the elements ofa film unit is a function of thecompressive pressure exerted on the film unit by the pressure-applyingmembers, the viscosity of the processing liquid and the speed ofmovement of the film assemblage through the convergent passage betweenthe pressure-applying members. In a handheld camera such as disclosed,it may be impossible to maintain the camera and film at a constanttemperature so that one of the factors, i.e., liquid viscosity,controlling the liquid spread thickness will constitute an independentvariable, while another factor, i.e., speed of movement of the film unitbetween the pressure-applying members, remains substantially constant sothat control over the thickness of the layer of processing liquiddistributed within a film unit can be achieved by controlling the thirdvariable, namely, the compressive pressure exerted on the film unit bythe pressure-applying members.

In the form of camera shown, the film unit is moved between thepressure-applying rolls to spread the processing liquid by advancing theleading end of the film unit, i.e., the container, into the bite of therolls and driving the rolls in frictional engagement with the film unit.The means for driving the rolls comprise an electric motor 64, a sourceof energy for the motor such as a battery or batteries 66, and atransmission in the form of gear train, including gears 68, 70, 72, 74and 76 for driving roll 60. A gear 78 may be coupled with roll 58 andmeshed with gear 76 on roll 60 for driving roll 58. The motor and thebatteries for powering the motor are designed to provide for advancementof a film unit between the rolls at a substantially constantpredetermined speed throughout the range of temperatures over which thecamera is likely to be employed. The housing includes an opening 80through which film units may be advanced by rolls 58 and 60 and means(not shown) are provided for moving each film unit, following exposurethereof, from exposure position within container 36 through slot 46 intothe bite ofrolls 58 and 60.

It has been found that the thickness of the layer of processing liquidspread within a film unit varies in inverse relation to the compressivepressure exerted on the film unit by the pressure-applying members sothat this thickness can be increased by reducing the compressivepressure and, conversely, decreased by increasing the compressivepressure. The thickness of the layer of liquid also varies directly withthe viscosity of the processing liquid and hence inversely as thetemperature of-the processing liquid. Accordingly, constant liquidspread thickness can be obtained by varying the compressive pressureinversely as to temperature; that is, by applying increased compressivepressure at lower temperatures to compensate for the increased viscosityof the liquid and applying reduced compressive pressure at highertemperatures to compensate for the reduced viscosity ofthe liquid.

In accordance with the invention, the camera includes means forautomatically sensing the ambient temperature and responding by varyingthe compressive pressure exerted by rolls 58 and 60 on the film unit ininverse relation to the temperature so as to maintain constant arelationship between I liquid viscosity and compressive pressure thatwill insure spreading of the processing liquid in a layer ofpredetermined depth even though the temperature and viscosity may vary.Such means may take the form shown, for example, in FIG. 2 and includetemperature-responsive means for automatically varying the effectivelength of each of cantilever springs 62 and thereby alter the biasexerted on rod 58 by the cantilever springs. In the form shown, thesetemperature-responsive means comprise a pair of elongated bars 82, eachpivotally mounted at one end adjacent rolls 58 and 60 and engaged at itsother end 84 with a medial portion of a spring 62 for imparting a biasto the spring. A fixed support member 86 is provided for engaging spring82 adjacent end 84 and supporting end 84 against spring 62. Bars 82 areformed of a material such as zinc-copper and zinc-cadmium alloys, havinga relatively high coefficient of thermal expansion so that the length ofeach bar will vary with temperature, thereby altering the position ofend 84 located in engagement with spring 62. The effective length ofeach spring 62 and hence, the force exerted by the spring, is a functionof the length of the spring between end 84 of bar 82 and roll 58, sothat by virtue of the construction shown, an increase in temperaturewill result in an increase in length of bars 82 and effective lengths ofsprings 62, thereby reducing the bias exerted by the springs on roll 58.

Another embodiment of temperature-responsive means for biasing rolls 58and 60 toward one another with a force inversely proportional to theambient temperature, is illustrated in FIG. 3. These means comprise apair of first elongated springs 88, each pivotally mounted at one end ona fixed stud 90 and engaged at its other end with roll 58, and a pair ofsecond springs 92, each pivotally mounted intermediate its ends on astud 90 and including a tab 94 on one end engaged with a medial portionof spring 88. Each spring 92 is biased in a counterclockwise directionviewing H6. 3, and cooperates with a spring 88 to effectively act as asingle spring biases about stud 90 in a counterclockwise direction. Theforce exerted by the rolls is varied by altering the deflection of thespring 92, specifically, by changing the position of end section 96 ofthe spring. Means for changing the position of end section 96 inresponse to changes in temperature comprise an elongated bar 98 formedof a material having a high thermal coefficient of expansion, mounted infixed position at one end near the rolls and extending toward endsection 96 of spring 92. Bar 98 includes a wedge-shaped end section 100slidably engaged between end section 96 and a fixed backing member 102for cooperating with the end section of spring 96 to pivot or deflectthe spring in response to temperature induced changes in the length ofbar 98. Thus, when the temperature is lowered, bar 98 will shrinkthereby, deflecting end section 96 of spring 92 away from fixed backingmember 102, increasing the force exerted on roll 58 by springs 88 and92. The reverse occurs when the ambient temperature rises so that bar 98increases in length and the deflection of spring 92 is reduced.

Another embodiment of the temperature-responsive means for varying thepressure exerted by the pressure-applying rolls is illustrated in FIG.4. In this embodiment, a pair of U-shaped springs 104 formed of abimetallic material, i.e., a laminate of two materials having differentthermal coefficients of expansion, are provided for biasing roll 58toward roll 60. One arm of each spring 104 is fixedly engaged within thecamera housing and the other arm is coupled with one end of roll 58 byan L- s ha'pe'dlllever 106 pivotally mounted intermediate it s ends,engaged at one end with roll 58 and engaged atits other end, with thefree armof spring 104. Thearms of'spring [04 are biased apart from oneanother'so as to pivot arm' 106' in a counterclockwise direction and thetwo materials comprising each bimetallic spring are selected such thatthe arms of the spring willtend to move apart from one another as thetem- .perature is reduced, thereby applying an additional force tendingto urge roll 58 toward roll 60. This is achieved by formingthebimetallic spring of two elements with the outer- 1 element having ahigher thermal coefficient of expansion than the inner clement, as'iswell known in the art.

Although the invention has been illustrated in connection with a pair ofpressure-applying members in the form of rolls,

with thefilm being moved between the rolls by rotation thereof,other'forms of pressure-applying members and other means formoving-thefilm through a passage between the pressure-applying membersare known in the art and are considered to fall within the scope of theinvention. Such other formsof pressure-applyingmembers "include, forexample nonrotatable members','in"which case, other means such as are 7well known'in the art are provided for pushing and/or pulling thefilmbetween the pressure-applying members. lt should be apparent alsothat othertemperature-responsive means may control spring tension anddeflection may be formed of a material having a very low temperaturethermal coefficient of expansion relative to the springs and camerahousing and it is in this" manner .that relative" movement of twoelements in response to temperature change, is achieved.

It should be noted and appreciated that the novel apparatus and processof the invention enable the performance, over a wide range oftemperature conditions, of a photographic process, particularly adiffusion transfer process, in which a viscous processing liquidcharacterized by a viscosity inversely proportional .to temperature isdistributed in a thin layer between a pair of 'sheetlike elements byadvancing the elements in superposition through a convergent passagebetween a pair of pressure-applying members; By virtue of the presentinvention, it is possible to achieve uniform liquid distribution of apredetermined thickness automatically and with relatively "simpleapparatus which lends itself to incorporation in compact, lightweight,portable cameras; and toemploy film structures including a minimum ofexcess processing liquid which as a result, do not requirec'omplexQexpensive and/or bulky components for collectingexcessprocessing liquid. The certainty with which uniform liquid distributionof predetermined thickness is obtained provides for consistent, reliableand high-quality results not obtainable with systems wherein the liquidspread thickness is subject to variations resulting from changes intemperature.

Since certain changes may be made in the above process and apparatuswithout departing from the scope of the invention herein involved, itis'intended that all matter contained in the above description or shownin the accompanying drawings shall be interpreted as illustrative andnot in a limiting sense.

' wherein said temperature-responsive means for varying the efspringmeans.

What I claimed is:

l. Photographic processingapparatus for treating an exposedphotosensitive element by distributing a liquid processing agent havinga viscosity which varies with temperature, as a thin layer in contactwith said photosensitive element, said apparatus comprising, incombination:

a pair of pressure-applying members providing a passage between saidmembers through which a photosensitive element and a second element aremovable in superposition to distribute a viscous processing agent in athin layer between said elements; l 1 t advancement meansfor moving saidelementsat substantially constant speed in superposition through saidpassage between said members; and temperature-responsive biasing meansfor urging said pressure-applying memberstoward one another with aforce. that'is an inverse function of the ambient temperature. 2.Photographic processing apparatus as defined in claim 1 wherein saidbiasing means include spring means and temperature-responsive means forvarying the effective length of said spring means.

3. Photographic processing apparatus as defined in claim 2 fectivelength of said spring means include an element mounted at one section ona portion of said apparatus in ffixed position relative to said springmeans, and including another section engaged with said spring means andat least an inter,-

1 mediate section formed of a material having a thermal coefficient ofexpansion substantiallydifferent from said spring means and portions ofmeans.

4. Photographic apparatus as defined in claim 3 wherein. said elementhas a relatively high thennal coefficient of expansion.

5. Photographic processing apparatus as definedin claim 1 wherein saidbiasing means include spring means and temperature-responsive means forvarying the deflection of said 6.'Photographic processing apparatus asdefined in claim 5 wherein,said temperature-responsive means for varyingthe deflection of said spring means include an element mounted at onesection on a portion of said apparatus in fixed position with respecttosaid spring means, and including another sec-.

tion engaged with said spring means and at least an intermediate sectionformed of a material having a thermal coefficient of expansionsubstantially different from said spring means and portions of saidapparatus mounting said spring means.

7. Photographic processing apparatus as defined in claim wherein saidelement has a relatively high thermal coefficient of expansion. i

8. Photographic processing apparatus as defined in claim 1 wherein saidbiasing means include spring means formed of a bimetallic material,which changes its configuration in responseto changes in temperature.

said apparatus mounting said spring

1. Photographic processing apparatus for treating an exposed photosensitive element by distributing a liquid processing agent having a viscosity which varies with temperature, as a thin layer in contact with said photosensitive element, said apparatus comprising, in combination: a pair of pressure-applying members providing a passage between said members through which a photosensitive element and a second element are movable in superposition to distribute a viscous processing agent in a thin layer between said elements; advancement means for moving said elements at substantially constant speed in superposition through said passage between said members; and temperature-responsive biasing means for urging said pressureapplying members toward one another with a force that is an inverse function of the ambient temperature.
 2. Photographic processing apparatus as defined in claim 1 wherein said biasing means include spring means and temperature-responsive means for varying the effective length of said spring means.
 3. Photographic processing apparatus as defined in claim 2 wherein said temperature-responsive means for varying the effective length of said spring means include an element mounted at one section on a portion of said apparatus in fixed position relative to said spring means, and including another section engaged with said spring means and at least an intermediate section formed of a material having a thermal coefficient of expansion substantially different from said spring means and portions of said apparatus mounting said spring means.
 4. Photographic apparatus as defined in claim 3 wherein said element has a relatively high thermal coefficient of expansion.
 5. Photographic processing apparatus as defined in claim 1 wherein said biasing means include spring means and temperature-responsive means for varying the deflection of said spring means.
 6. Photographic processing apparatus as defined in claim 5 wherein said temperature-responsive means for varying the deflection of said spring means include an element mounted at one section on a portion of said apparatus in fixed position with respect to said spring means, and including another section engaged with said spring means and at least an intermediate section formed of a material having a thermal coefficient of expansion substantially different from said spring means and portions of said apparatus mounting said spring means.
 7. Photographic processing apparatus as defined in claim 6 wherein said element has a relatively high thermal coefficient of expansion.
 8. Photographic processing apparatus as defined in claim 1 wherein said biasing means include spring means formed of a bimetallic material which changes its configuration in response to changes in temperature. 